A graded doping technique was presented to fabricate high brightness and high efficiency OLEDs, in which a copper phthalocyanine(CuPc) film acts as buffer layer (alpha) -naphthylphenybiphenyl amine(NPB) film as hole-transport layer and a tris(8-hydroxyquinolinolate)aluminum(Alq3) film as the electron-transport layer.The luminescent layer consists of the mixture of NPB,Alq3 and an emitting dopant 5,6,11,12-petraphenylnaphthacene(Rubrene), where the concentration of NPB raised while the concentration of Alq3 was declined gradually in the deposition process. The graded doping device exhibited the maximum emission of 50000cd/m2 at 35v and the maximum efficiency of about 8cd/A at 9v, respectively, which have been improved by four times in comparison with the conventional doped devices.
An organic quantum-well structure electroluminescent device is fabricated by a doping method. The quantum-well structure consists of (formula available in paper) as potential well and emitter, undoped NPB as a barrier potential. Compared with a conventional doping structure device, both the maximum brightness and electroluminescent (EL) efficiency of the device are enhanced, reaching 40 000 cd/m2 and 5.6 cd/A, respectively. Especially, with the increase of the drive voltage, the EL efficiency (cd/A), after reaching its maximum, declines very slowly, almost independent of the drive voltage in a wide range from 5V to 13V. The characteristic may be useful in improving the lifetime of the device.
A white light-emitting organic/polymeric electroluminescent (EL) device with multilayer thin-film structure is demonstrated. The device structure of glass substrate/indium-tin oxide/poly(N- vinylcarbazole)/phenylpyridine beryllium(BePP2)/8- (quinolinolate)-aluminum (Alq) doped with 5,6,11,12- petraphenylnaphthacene/Alq/LiF/Al was employed. The turn-on voltage is as low as 2.9 V. Blue fluorescent BePP2 yellow fluorescent rubrene, and green fluorescent Alq are used as three primary colors. The Commission Internationale de l'Eclariage coordinates of the emitted light are at 10V, which is located in the white-light region. Bright white light, over 6800cd/m2, was successfully obtained at about 17V, and the maximum efficiency reaches to 1.38m/W at 8.5V.
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